Victoria's premier trainer Darren Weir will face a penalty hearing where he could be fined up to $5000 over a positive swab.
A Weir-trained horse tested positive at the Burrumbeet jump-outs.
Air Guitar returned a positive swab to phenylbutazone and oxyphenbutazone on June 22.
Weir has said he would plead guilty to the charge at a hearing in Ballarat on Thursday, allowing stewards will proceed under a local rule of racing and can issue a fine of no more than $5000.
Trainers Simon Morrish and Henry Dwyer have indicated they will also plead guilty when they front stewards after horses they train also returned positive swabs from the same set of jump-outs.